Electron microscopy specimens (also referred to in short as microscopy specimens below) have dimensions that lie in the sub-millimeter range, i.e., in the range of a few micrometers (μm) or nanometers (nm). Usually, these specimens are examined in an electron microscope (scanning electron microscope or transmission electron microscope, TEM) or in an ion microscope or in other devices with a similar resolution.
Such specimens may have different configurations. An example of an often-used microscopic specimen is a TEM lamella, which is involved for transmission electron microscopy. TEM lamellas are so thin that, at least in portions, they are transmissive to electrons. Therefore, the electron-transparent specimen regions can be passed by electrons within the scope of the examination in the transmission electron microscope (TEM) such that transmitted electrons can be detected and used for image production purposes.
So that TEM lamellas contain the specimen region of interest (ROI), they are, in general, be prepared from the full specimen material, i.e., from a specimen block. The TEM lamella is severed and removed from the specimen block by way of a so-called lift out so that it is then examined in a different device, preferably a TEM.
In general, a distinction is made in the microscopic specimen preparation between ex situ methods and in situ methods, depending on the type of lift out.
In the case of an ex situ lift out, a specimen region of interest, which is still situated in the specimen block, is initially thinned using a focused ion beam (FIB) in an FIB device. That is to say, material is ablated with the ion beam until the specimen has the desired lamella thickness and said specimen is present as an electron-transparent lamella. Then, the ion beam is used to cut the side edges of the TEM lamella free such that the TEM lamella is largely exposed. In the next step, the entire specimen block, together with the TEM lamella, is removed from the FIB device and transferred into a light microscope. There, a glass tip is fastened to the TEM lamella with the aid of a micromanipulator. The TEM lamella can now be detached from the specimen block and transferred to a TEM grid or any other suitable specimen holder via the micromanipulator. The TEM grid with the TEM lamella is then transferred into the TEM for further examination.
In the case of the in situ lift out, the region of the future TEM lamella is initially freely prepared with the ion beam in broad brushes. The TEM lamella is released from the specimen block via a micromanipulator, which is attached to the FIB device, held in the specimen chamber of the FIB device and thinned to the desired lamella thickness by way of the ion beam. Finally, the TEM lamella is placed on a TEM grid or the like and fastened where desired, and it thus can be transferred from the FIB device into the TEM.
In the ex situ lift out, the specimen block is therefore situated outside of the FIB device when
the microscopic specimen is severed from the specimen block, whereas this occurs within the FIB device in the in situ methods. What is common to both methods is that special manipulation tools such as micromanipulators, micro grippers or needles are involved.Some methods additionally involve apparatuses for introducing process gases such that substances can be deposited in a targeted manner, said substances allowing the prepared microscopic specimen to be fastened to a glass tip or a metal needle, for example. Moreover, the user should have a certain amount of experience of handling the tools and experimental skill in order to successfully prepare the specimens within a justifiable amount of time.
Therefore, in many applications in electron microscopy and ion microscopy, it would be advantageous to be able to release selected small structures or specimen regions in a contactless manner from the specimen block from which they are obtained in order to thus make said small structures or specimen regions accessible to the further examination or processing.
Various methods of TEM lamella preparation are known. Thus, different types of FIB lift out techniques (ex situ and in situ) have been described for the defect analysis of wafers (Giannuzzi et al., 2002; Giannuzzi & Stevie, 1999).
Additionally, improved methods for the in situ lift out of TEM specimens with the aid of a two-beam device (Langford & Rogers, 2007; Tomus & Ng, 2013) are known.
EP1998356 A2 describes a method for an in situ STEM specimen preparation via an SEM-FIB combination device, which makes do without a flip stage.
Moreover, a method for the three-dimensional nano fabrication of thermoplastic polymers via FIB has been described.
Langford et al. (2000) disclose a cantilever technique for the TEM lamella production, in which the specimen block is removed from the FIB device in order to sever the prepared cantilever from the specimen block by the application of force.
Moreover, methods have been described for shaping microscopically small structures with micro and nano tools (so-called “nano forging”).
The following documents should be considered:                EP 1998356 A2        Landefeld, A., Rösier J (2014): Beilstein J. Nanotechnol. 5: 1066-1070        Giannuzzi et al (2002): Microelectronic Failure Analysis Desk Reference 2202 Supplement        Giannuzzi & Stevie (1999): Micron 30: 197-204        Langford & Rogers (2007)        Langford et al. (2000): J. Vac. Sci Technol. B 18(1)        Tomus & Ng (2013): Micron 44: 115-119        Lee et al. (2012): Journal of Microscopy 224, 129-139        